You don’t need a valid license to run a Windows 10 Insider Preview Build on your PC. Each build is time-limited, but a new version will be released before the previous one expires.

Provided you keep updating your system to the latest build, you’ll have no problems. However, if you’ve installed a preview build and not updated it — hey, free Windows! — Microsoft is about to flip a kill switch that will stop it working entirely.

If you’re running the Windows 10 Anniversary Update (Build 14393) in either the Slow or Release Preview rings you’ll be able to continue to do so without problems and won’t see an expiration notification.